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05.06.2015 09:03 Age: 9 yrs

[Saral/AltiKa]: recent orbit drift

Category: Operational news

Saral/AltiKa’s ground track has been drifting from the nominal track with deviations than can reach more than 10km depending on the latitude

Due to reaction wheel issues, Saral station keeping maneuvers have not been performed nominally since March 31st, 2015.

Below is a list of recent station keeping events:

  • March 31st, 13:50, station keeping maneuver; velocity variation twice more than expected due to reaction wheel issue, resulting in a faster than expected westward drift of the ground track,
  • April 9th, 12:28, station keeping maneuver; to correct the westward drift,
  • May 1st, 12:36, station keeping maneuver; aborted due to reaction wheel issue,
  • May 26th, 12:51, station keeping maneuver; unexpected thruster firing from 10:00 to 10:04 to control a reaction wheel error, during the maneuver guidance was performed with thrusters instead of reaction wheels. The velocity variation was twice less than expected.
  • June 3rd, 11:59, station keeping maneuver planned to calibrate satellite rotation with thrusters; aborted by ISRO.

As a result, Saral/AltiKa’s ground track has been drifting from the nominal track with deviations than can reach more than 10km depending on the latitude. The following graphs (estimated from IGDR data) display the current situation of SaralAltiKa’s ground track drift at different latitudes.
The current orbit drift is eastward (from April 9th onwards). On the graphs corresponding to latitudes 45°N and 66°N, the cross-track distance is oriented according to the satellite along-track velocity, thus the sign change between even and odd passes.

<media 14558 750x550 - "IMAGE, 201506 Saral Cross Track Distance, 201506_Saral_CrossTrackDistance.png, 41 KB"></media><media 14560 750x550 - "IMAGE, 201506 Saral Suivi Dcross Track Lat45, 201506_Saral_SuiviDcrossTrack_Lat45.png, 54 KB"></media>
<media 14562 750x550 - "IMAGE, 201506 Saral Suivi Dcross Track Lat66, 201506_Saral_SuiviDcrossTrack_Lat66.png, 67 KB"></media>
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